1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus, and more particularly, to a magnetron sputtering apparatus with improvements in deposition rate and film uniformity.
2. Description of the Related Art
Generally, physical vapor deposition (PVD) and chemical vapor deposition (CVD) are widely used for the deposition of films with a small thickness. The CVD is a process that forms thin films with desired physical properties using chemical reaction. The PVD is a process that forms thin films by imparting a momentum to target materials in order for the target materials to travel toward a substrate.
The PVD can be largely classified into magnetron sputtering and evaporation. The evaporation is a method that heats a solid or a liquid to be decomposed into molecules or atoms and then solidifies them on a surface of a substrate. The evaporation has been widely used because an apparatus therefor has a simple structure and a large amount of evaporation materials can be easily used.
The sputtering is a method that leads to collision of high-energy particles with sputtering targets to deposit materials ejected from the sputtering targets on a substrate. The sputtering has advantages in that thin films can be formed to a uniform thickness over a wide area, and the composition ratio of alloy thin films can be easily adjusted compared to other deposition processes. Therefore, the sputtering has been widely used in fabrication of semiconductor devices such as dynamic random access memory (DRAM), static RAM (SRAM), nonvolatile memory (NVM), and LOGIC, or other electronic devices.
Magnetron sputtering using a magnetic field can be carried out in a reaction chamber having a process condition of a low pressure and high-density plasma. Therefore, sputtering particles can easily advance forward, and thus, can be efficiently deposited even on stepped portions, thereby enhancing step coverage.
FIG. 1 is a schematic sectional view of a conventional magnetron sputtering apparatus.
Referring to FIG. 1, a substrate 17 and a substrate holder 19 supporting the substrate are disposed in a vacuum chamber 21. A target 11 is disposed on the opposite side from the substrate 17. Magnets 15 are disposed behind the target 11 to form magnetic field lines of predetermined directions. In addition, a power supply unit 27 is disposed outside the vacuum chamber 21 to apply a voltage to an electrode 13 on which the target 11 is disposed.
When a predetermined vacuum is maintained in the chamber 21, an inlet gas such as argon is supplied to in the chamber 21 and electric discharge occurs by a negative voltage applied to the electrode 13. As a result, plasma consisting of gaseous ions, neutral molecules, and electrons is generated. The gaseous ions are accelerated by a negative voltage and collide with the target 11. Due to the collision, surface atoms of the target 11 gain momentum, thereby resulting in ejection of the surface atoms from the target 11. Therefore, the ejected atoms are deposited in a thin film on the substrate 17. In this case, the thickness of the deposited thin film is determined by an applied voltage, pressure, a deposition time, and the like.
However, it is known that it is difficult to efficiently control the momentum of charged particles, determining the sputtering efficiency in magnetron sputtering. When a horizontal magnetic field is concentrated on a specific area, the target 11 is non-uniformly eroded and the particles of the target 11 are also deposited to a non-uniform thickness on the substrate 17. In addition, although demands for highly integrated devices, narrow line width, and large process wafers increase continuously, it is difficult to satisfy such demands using a sputtering apparatus comprising a conventional magnetron cathode.
It is reported that a magnetron sputtering process using a magnetron moving system provides excellent film uniformity. However, a conventional magnetron cathode exhibits non-uniform magnetic field distribution, as shown in FIG. 2. FIG. 2 shows the magnetic field line distribution of a conventional magnetron cathode.
Referring to FIG. 2, a magnetron cathode has a width of 24 mm and is disposed behind a target having a width of about 40 mm. While the density of magnetic field lines originating from the magnetron cathode is high at the center area of the magnetron cathode, it decreases as the lines it goes away from the center area. The density of magnetic field lines is the highest at a 12 mm radial distance (r=12 mm) from the axial line (r=0) of the magnetron cathode, thereby producing the highest magnetic field. At the surface of the target, i.e., when z is 6 mm, the density of magnetic field lines is the highest at r=0 at which the intensity of magnetic field is maximal. As r increases, the density of magnetic field decreases. Therefore, the surface of the target exhibits non-uniform magnetic field line distribution. Such non-uniform magnetic field line distribution leads to an non-uniform erosion profile as shown in FIG. 3.
FIG. 3 is a graph of an erosion profile according to a distance from the center (x=0) of a target using the magnetron cathode of FIG. 2. In detail, FIG. 3 shows a change in erosion profile according to a distance from the center of the target at varying erosion powers of (a) 0.027 kWhcm−2, (b) 0.051 kWhcm−2, and (c) 0.099 kWhcm−2.
Referring to FIG. 3, all of the graphs (a), (b), and (c) exhibits the deepest erosion profile at a 3 cm distance from the center (x=0) of the target. As an erosion power increases, the target is more deeply eroded. Here, comparative values to the distance X are represented at the top of the graph.
FIG. 4 is a photograph of a target eroded in a conventional sputtering apparatus comprising a conventional magnetron cathode.
Referring to FIG. 4, a narrow, ring-shaped erosion area is observed. In the erosion area, the degree of erosion is high relative to the other areas of the target, thereby resulting in unbalanced erosion profile.
Such a magnetron cathode technology has following problems in a current sputtering process requiring a small line width (0.14 μm or less) and high aspect ratio (5:1 or more): deposition occurs asymmetrically, film uniformity is poor, and target erosion occurs locally, thereby decreasing the efficiency of materials used.